In general, repeaters are installed in areas in which signals transmitted from a main transmitter are weak in order to solve unstable reception and expand the transmission range of the signals.
When receiving a signal from the main transmitter, the repeater frequency down-converts the received signal to an intermediate frequency signal and up-converts to the intermediate frequency signal again, and then up-converts the intermediate frequency signal to a frequency corresponding to an output frequency. In this instance, the repeater can use a frequency that is different from an input frequency for receiving the signal from the main transmitter as an output frequency.
When the input frequency and output frequency of the repeater are different from each other, the repeater should generate a tone signal to be mixed with an intermediate frequency signal in order to generate an output frequency that equals the input frequency of the repeater. When the tone signal is generated by using an output signal of a local oscillator that has a frequency error, the tone signal frequency becomes inaccurate, thereby deteriorating accuracy of the output frequency.
In order to solve such a problem, the repeater generates the tone signal from a symbol or a sample clock obtained by performing symbol timing synchronization on the signal of the main transmitter, or generates the tone signal from a global positioning system (GPS) clock signal obtained by using the GPS. However, a frequency multiplication ratio between a symbol timing frequency and the output frequency is too high so that a very high output frequency jitter is caused by a timing jitter generated from the symbol timing synchronization process of the repeater. Accordingly, an unstable output frequency is obtained. Further, since different repeaters respectively have independent jitters, a receiver that simultaneously receives signals from two or more repeaters is deteriorated in receiving performance.
The GPS clock signal may be relatively more stable than the symbol or sample clock, but the GPS clock signal is not sufficiently accurate so that repeater manufacturing cost increases to improve the accuracy. Therefore, a method for reducing the timing jitter effect is needed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.